'Topping' christmas Tree

I would not do it. Cutting the top odd will cause stress and an entryway for fungus and other diseases. It will also promote poor growth such as multiple leadering. From my point of view the idea of obtaining a potted Christmas trees is to foster stewardship of trees by planting it. You may plant it on your property, or give it to a friend who can, or even donate it to a local parks commission for planting on public land. Of course you may have intended to plant the tree all along but I just thought that I might mention this. A belated Merry Christmas to You and Happy New Year!

As Loosestrife has already stated cutting out the leader will result in multiple leaders and a very odd looking tree. Now the Festive Season is over it needs to be planted in the ground, though that can wait for a month it you ground is waterlogged or frozen.

Be aware how big they grow......

Depends which 'Christmas' tree it is Pamg

Just in case you aren't a gardener, multiple leaders in practice means it will get fat and bushy instead of tall and straight, so will not look like a "christmas tree"

Nope just a mess Stera...

True Mg but unless its a dwarf variety its going to be big!

Picea abies and Abies procera will grow to 180 feet in 20 to 50 years or so.
I have both growing in our Millenium wood, the Abies procera was root wrapped and in a pot for a number of years before planting out in 2000, its too tall now for the tallest ladder, the Picea I grew from seed and seems slower growing, its taller than me now....
we have Abies balsamea too, slow growing and less tall....lovely cones, there is a dwarfer variety hudsonia I think......

We bought a Picea glauca conica in a pot and, provided it was correctly named, it will take around 25 years to grow to 7 foot. Time will tell!

I just googled it Mg, what a pretty tree, looks a perfect shape....
you probably guessed I have a thing for trees.....

Me too Pamg so fingers crossed it will behave. We'd thought to use it in the house at Christmas time but realised it wouldn't like the warmth.